Add integration test for destroy_units

Author: cderici

tests/integration/test_model.py

@@ -882,6 +882,23 @@ async def test_wait_for_idle_with_exact_units_scale_down_zero(event_loop):
         assert (end_time - start_time) > 0.001
 
 
+@base.bootstrapped
+@pytest.mark.asyncio
+async def test_destroy_units(event_loop):
+    async with base.CleanModel() as model:
+        app = await model.deploy(
+            'ubuntu',
+            application_name='ubuntu',
+            series='jammy',
+            channel='stable',
+            num_units=3,
+        )
+        await model.wait_for_idle(status='active')
+        await model.destroy_units(*[u.name for u in app.units])
+        await model.wait_for_idle(timeout=5 * 60, wait_for_exact_units=0)
+        assert app.units == []
+
+
 @base.bootstrapped
 @pytest.mark.asyncio
 async def test_watcher_reconnect(event_loop):